Q18 of 249 Page 31

Find the probability that the sum of the numbers showing on two dice is 8, given that least one die does not show five.

We know, when a pair of dice is thrown, total possible outcomes are = 36


A=No of outcomes for getting sum of 8 are


{(2,6),(3,5),(4,4),(5,3),(6,2)} = 5


Therefore, P(A) =


B= No of outcomes for at least one die does not show 5


= {(1,1),(1,2),(1,3),(1,4),(1,6),(2,1),(2,2),(2,3),(2,4),(2,6),(3,1),(3,2),(3,3),(3,4),(3,6),(4,1),(4,2),


(4,3),(4,4),(4,6),(6,1),(6,2),(6,3),(6,4),(6,6) } = 25


Hence P(B) =


(A B) = outcomes of getting sum as 8 with at least one die not showing 5


= {(2,6),(4,4),(6,2)= 3


Hence P(A B) =


Therefore, =


(answer)


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